Naturally occurring carbohydrate (i.e. sugar) sweeteners such as sucrose are still the most widely used sweetening agents. Sucrose is paramount among sweet compounds in that it produces sweetness that is unmasked by any other taste sensation. However, relatively large amounts of sucrose are used in sweetened foods, beverages, and medicines, and it is now accepted that sucrose is the main dietary source of dental caries in developed countries. While these naturally occurring carbohydrates generally fulfill the requirements of sweet taste, the abundant usage thereof does not occur without deleterious consequences such as high caloric intake and nutritional imbalance. In fact, often the level of these sweeteners required in foodstuffs is far greater than the level of the sweetener that is desired for economic, dietetic or other financial consideration. Therefore, there is much interest in discovering sugar substitutes that are highly sweet, and are also noncariogenic, noncaloric, nontoxic, and nonmutagenic, and exhibit acceptable taste characteristics, and solubility and stability profiles.
At the present time, only saccharin, aspartame, and acesulfame K are currently approved as intensely sweet sucrose substitutes in the United States and questions have been raised about the suitability of all of these substances. For example, many of these artificial sweeteners have the disadvantages of high cost, as well as delay in the perception of the sweet taste, persistent lingering of the sweet taste, and very objectionable bitter, metallic aftertaste when used in food products.
However, plants represent an alternative resource pool for the isolation and development of new high-intensity sweetening agents, and about 15 compound classes of plant-derived "natural" sweeteners are now known. In Japan, the natural sweeteners glycyrrhizin, stevioside, and thaumatin are all used as approved sucrose substitutes in the diet, while in the United Stated there is much public demand for natural substances, and much effort is currently being expended in the quest for additional naturally occurring sweeteners.
The plant genus Abrus belongs to the legume subfamily, Papilionoideae, which is constituted by up to 12 tropical species. One of the most widely distributed species in the genus, Abrus precatorius L. is native to India, and is also found in tropical and subtropical regions of Africa, Southeast Asia, Florida, Hawaii, and the West Indies. The plant is a vine that has leaves up to 4 inches long, and has many common names, including "Indian licorice", "Jamaica licorice", and "wild licorice". While the bright red seeds of A. precatorius are poisonous, the roots and leaves evidence no toxicity, and have a long history of human internal consumption, particularly as a licorice substitute. (Licorice is the source of the sweet triterpene glycoside, glycyrrhizin.) The leaves of A. precatorius have been found to be sweeter than the roots, and the presence of glycyrrhizin had been previously claimed by several authors to account for the sweetness of the leaves, in levels of as much as 9%. See, e.g., Hooper, Pharm. J. Trans. Third Ser. 24: 937-938, 1894; Akinloye, et al., Nigerian J. Pharm., 12:405, 1981. Another species in this genus is Abrus fruticulosus which can also be found in Africa and Southeast Asia. The roots of this species have been used to treat digestive disorders.
The present invention reveals the presence of a new class of triterpene glycosides, the abrusosides, and in particular abrusosides A, B, C and D which are found in the genus Abrus. More specifically, these abrusosides can be isolated from A. precatorius and A. fruticulosus. All of these abrusosides are based on the aglycone, abrusogenin, which exhibits a unique carbon skeleton, not found in nature or derived synthetically to date. The sweetness of the genus Abrus (more specifically, A. precatorius and A. fruticulosus) can be ascribed solely to the abrusosides.
The present invention relates to the use of Abrusosides A-D as sugar substitutes and in particular, contemplates utilizing these abrusosides as replacements for sugars and other known natural sweeteners or sugar substitutes such as glycyrrhizin, stevioside, thaumatin, as well as the synthetic sweeteners, saccharin, aspartame, and acesulfame K.
Glycyrrhizin, for example, which has been used in various forms as a sweetener (i.e., ammoniated glycyrrhizin, glycyrrhizin, and its salt), has known adrenocorticomimetic activity (i.e., it mimics the effects of the adrenal cortex) which can cause abnormal retention of sodium, chlorine and water in humans, and this tends to limit the amount of the latter compounds that can be consumed. The abrusosides of the present invention do not exhibit these limitations.
The production of the abrusosides of the present invention can further be economically competitive with the production of other natural sugar substitutes.